Change hard-coded temporary directory.

The properties tests creates a temporary directory in /data/nativetest,
but this directory might not exist in all circumstances.
Change this to create the temporary directory in /data/local/tmp.

Change-Id: I812d3e24fcd084c5d74055c9faa95b1656f255bc
diff --git a/tests/system_properties_test.cpp b/tests/system_properties_test.cpp
index 9602607..ba73c68 100644
--- a/tests/system_properties_test.cpp
+++ b/tests/system_properties_test.cpp
@@ -28,10 +28,10 @@
 
 struct LocalPropertyTestState {
     LocalPropertyTestState() : valid(false) {
-        char dir_template[] = "/data/nativetest/prop-XXXXXX";
+        char dir_template[] = "/data/local/tmp/prop-XXXXXX";
         char *dirname = mkdtemp(dir_template);
         if (!dirname) {
-            perror("making temp file for test state failed (is /data/nativetest writable?)");
+            perror("making temp file for test state failed (is /data/local/tmp writable?)");
             return;
         }